Target .NET 8 (LTS) as well as .NET 10 #57

Summary

The CLI and ShellUI.Components target .NET 10 only. Many teams are on .NET 8 (LTS).

Notes

• The CLI and Components compile once TargetFrameworks is net8.0;net10.0 and Microsoft.AspNetCore.Components.Web is referenced per framework (8.0.x / 10.0.x).
• The generated templates already compile on net8.
• Cost: a CI matrix that builds and tests both frameworks.